1. Field of the Invention
The present invention relates to a functional molecule that shows a high affinity to various targets (targeted material), is easily amplified and replicated, is suitable for a wide range of fields such as drugs, drug delivery, biosensors, regulation of gene expression amount, conquest of diseases caused by an abnormal gene, elucidation of the function of the protein into which a gene is translated and development of reaction catalysts, and particularly suitable for analysis of the protein, and relates to a process for producing the same.
2. Description of the Related Art
In 2002, a draft of human whole gene information was published and in 2003, perfect information thereof is in a schedule to be elucidated. As a result, a central interest of researchers and scientists has shifted to an analysis of a protein being a gene product by a gene. The analysis of the protein become naturally possible by a presence of a molecule having an affinity to individual proteins targeted. Many kinds of proteins targeted for the analysis are present in a cell and many of them have completely unknown amino acid sequence and structure thereof. Therefore, many kinds of molecules are required for the analysis of the proteins.
However, at present, no process effective for preparing or obtaining the molecule used for the protein analysis has been known. The most common process, which has been known so far and is applied for obtaining the molecule having the affinity to a specific protein, is a process to select an affinity antibody by using an animal immune system. However, in this process, use of an animal requires a large amount of the protein, more number of steps, and a high cost. In addition, although the affinity antibody obtained through selection by this process can be replicated by making it as a monoclonal antibody followed by maintaining the cell, it requires a high cost and cannot be improved. Further, there is a problem in that only an affinity antibody having an affinity to the identical target can be selected. Therefore, selecting and obtaining each affinity antibody having an affinity to all kinds of proteins present in the cell is very difficult.
Recently many studies are conducted on selection of a molecule having a specific function from a nucleotide random sequence to identify the molecule on the basis of gene information thereof. As the result, many reports describe molecules having an affinity to a specific target and RNAs catalyzing a specific reaction.
However, a compositional unit number of a nucleotide is 4 in both RNA and DNA and, thus, kinds of functional groups present in a polymer thereof are very limited to limit naturally functions thereof. In order to solve this problem, a study by using a modified nucleotide has been carried out. However determining that a molecule, in which a specific site has received selectively a certain nucleotide, is the molecule requires removing a natural nucleotide, which is corresponding to the modified nucleotide, from an experimental system. As the result, the compositional unit number of the nucleotide is 4+1−1=4 making a radical solution impossible. Further, RNA is enzymatically very unstable and, thus, an attempt to synthesize a molecule having the same function by using a DNA, which is enzymatically stable, has been failed. In these cases, a molecule having an affinity to a specific target is obtained by repeated operation of amplification and purification and, therefore, it is at present difficult to synthesize many kinds of molecules.
On the other hand, in a study by using amino acid or an artificial material as a compositional unit to select the molecular by combinatorial chemistry, gene information, which is not contained in the molecule itself composed of the compositional unit, does not allow amplifying the sequence information. Therefore, determining the sequence of the molecule requires many steps.
Meanwhile, concerning the synthesis of the protein having the gene information, there is the study in which puromycin was introduced to a 3′ terminal of an mRNA (e.g., refer to Japanese Patent Application Laid-Open (JP-A) No. 2002-291491). This study was carried out by applying the property that puromycin is misunderstood as the amino acid in a translation system and apt to be incorporated easily in the protein. However, in this case, so far, an efficiency of puromycin incorporation is very low and, hence, there is only a report describing that the molecule was selected from a library of a random 3 residues of amino acids. Moreover, there is the problem in that even if the efficiency of puromycin incorporation is improved, the number of a library pool possible finally to become the protein having the gene information in a DNA random pool is very small. Such problem arises from the fact that a termination codon is present on a DNA random sequence in a proportion of 3/64 and a rare codon which is not preferred by the cell is present.